The present invention relates to an optical recording/reproducing apparatus in which a disk is irradiated with a laser beam to thereby perform both recording and reproducing of information on the disk.
Recently, various examples of such recording/reproducing systems have become known. Japanese Unexamined Patent Publication No. 61-42735 discloses a method of estimating the lifetime of a disk of a type for which information recording/reproducing is performed by using a change in phase (between crystalline and amorphous) of the material constituting the recording surface of the disk.
According to the method disclosed in this publication, a synchronizing signal is recorded on an outer circumferential track of the disk at initialization. Also during the initialization process, the synchronizing signal is reproduced and the amplitude of the reproduced signal measured and recorded on the disk. After the disk has been placed in service, to estimate its remaining service life at any point in time, the recorded value is read out and compared with the present value of the amplitude of the reproduced signal. When the value of the amplitude of the reproduced signal falls below a predetermined level in comparison with the recorded value of the amplitude at initialization, it is judged that the useful life of the disk is over.
The method, however, has the disadvantage that it is necessary to record predetermined information, such as a synchronizing signal, when initialization is carried out, thereby reducing the area available for other recording. The method has a further disadvantage in that it is impossible to account for deterioration of the recording material of the disk in the period prior to initialization.